President Donald Trump declared he's willing to take on the National Rifle Association over gun legislation, but Republicans who control Congress aren't so sure. They prefer to consider only modest changes to firearms limits in response to the mass shooting at a Florida high school.

Congress returned to work Monday without following Trump's lead on any of the major initiatives he has tossed into the debate since the massacre at Marjory Stoneman Douglas High School.

Despite public calls for stricter gun laws, Republican leaders have largely kept quiet after the shooting which left 17 dead and ushered in another phase in the gun debate, prompted in large part by the activism of the young survivors. Some students visited with lawmakers Monday.

Over the weekend, Trump spent time talking to Republican House Speaker Paul Ryan of Wisconsin, and the White House is inviting lawmakers from both parties for meetings this week. But Trump's ideas to arm many teachers, lift the minimum age for purchasing assault rifles to 21 and impose stricter background checks were falling flat.

"You guys, half of you are so afraid of the NRA," the president said Monday at a meeting with the nation's governors. "There's nothing to be afraid of. And you know what? If they're not with you, we have to fight them every once in a while. That's OK."

Instead, Senate Republicans are hoping to consider more modest legislation from Sens. John Cornyn, R-Texas, and Chris Murphy, D-Conn., to strengthen the National Instant Criminal Background Check System, or NICS. The "Fix NICS" bill, similar to one approved last year in the House, would penalize federal agencies that don't properly report required records used to determine whether someone can legally buy a gun.

Cornyn, the Senate's No. 2 Republican, questioned Trump's proposal to raise the age limit for assault weapons, noting that the minimum age to enlist in the military is 18.

"I'm not sure I understand the 21 age. I think there are better ways to address it than just an arbitrary age increase," he told The Washington Times.

Trump insisted Monday that sometimes political leaders need to buck the NRA, which builds its political power by major campaign spending and motivating gun rights supporters to vote. Though he did not mention increasing the minimum age for rifle purchases, he wants to toughen the Cornyn bill with stricter background checks, a change the NRA has opposed.

"We're going to strengthen it," Trump said. "We're going to make it more pertinent to what we're discussing."

Democrats have long pressed for more sweeping changes toward a universal background check system, including requiring inquiries for online and gun show purchases.

Senate Minority Leader Chuck Schumer of New York said Monday that if all Congress can accomplish is passage of the "Fix NICS" bill "it would be an abject failure and a dereliction of our duty."

Sens. Joe Manchin, D-W.Va., and Pat Toomey, R-Pa., are reviving their background check bill, which failed earlier, including after the Sandy Hook Elementary School shooting in 2012. Manchin said opponents at the time worried then-President Barack Obama would impose even stricter restrictions. "Well they're not having that fear right now with President Trump," he said.

In the House, many Democrats want to reinstate an assault weapons ban that expired more than a decade ago.

But House Republican leaders believe it's up to the Senate to take the next steps, according to a top House GOP aide, who spoke only on condition of anonymity because he wasn't authorized to discuss legislative strategy.

The House passed legislation in December that included changes to the background-check system. It was part of a broader package that stalled in the Senate because it included expanded gun rights by requiring states to recognize conceal-carry permits issued by other states.

The House package also included a measure to study bump stocks, the devices that turn rifles into automatic-style weapons and were used in the Las Vegas assault last fall, the deadliest mass shooting in U.S. history.

In the Senate, Republican leaders see the best route to passage in separating the issues of background checks and state reciprocity measures. They were testing support Monday for quick consideration of the background checks bill, which was introduced last fall after the shooting of churchgoers in Texas. At the time, authorities acknowledged having failed to report the Texas gunman's domestic violence conviction to the National Criminal Information Center database.

"I'm for doing what's achievable," Cornyn told reporters.

But even the "Fix NICS" bill faced resistance from some in the GOP ranks.

At the same time, some Republican lawmakers appeared willing to go further, particularly in outlawing bump stocks, which the Trump administration wants to do through administrative action as the NRA prefers, rather than legislation.

Rep. Ryan Costello of Pennsylvania said he supports a ban on bump stocks, whether it's done through legislation or a change in federal regulations.

"That's sort of simple stuff that we should get done for the American public," he told The Associated Press.

Costello, who faces a stiff re-election challenge in a district that has been redrawn to favor Democrats, also supports the Fix NICS bill and a measure to raise age limits on purchases of certain assault weapons.

At the White House, Washington Gov. Jay Inslee, one of two Democrats to address Trump publicly, expressed his concerns over the idea of arming teachers as a response to the school shootings. "We need a little less tweeting, a little more listening," Inslee said.